The present invention in one aspect relates to removal of selected gases from air. The invention has particular utility for the extraction of carbon dioxide (CO2) from air and will be described in connection with such utilities, although other utilities are contemplated, including the sequestration of other gases including NOx and SO2.
There is compelling evidence to suggest that there is a strong correlation between the sharply increasing levels of atmospheric CO2 with a commensurate increase in global surface temperatures. This effect is commonly known as Global Warming. Of the various sources of the CO2 emissions, there are a vast number of small, widely distributed emitters that are impractical to mitigate at the source. Additionally, large scale emitters such as hydrocarbon-fueled power plants are not fully protected from exhausting CO2 into the atmosphere. Combined, these major sources, as well as others, have lead to the creation of a sharply increasing rate of atmospheric CO2 concentration. Until all emitters are corrected at their source, other technologies are required to capture the increasing, albeit relatively low, background levels of atmospheric CO2. Efforts are underway to augment existing emissions reducing technologies as well as the development of new and novel techniques for the direct capture of ambient CO2. These efforts require methodologies to manage the resulting concentrated waste streams of CO2 in such a manner as to prevent its reintroduction to the atmosphere.
The production of CO2 occurs in a variety of industrial applications such as the generation of electricity power plants from coal and in the use of hydrocarbons that are typically the main components of fuels that are combusted in combustion devices, such as engines. Exhaust gas discharged from such combustion devices contains CO2 gas, which at present is simply released to the atmosphere. However, as greenhouse gas concerns mount, CO2 emissions from all sources will have to be curtailed. For mobile sources the best option is likely to be the collection of CO2 directly from the air rather than from the mobile combustion device in a car or an airplane. The advantage of removing CO2 from air is that it eliminates the need for storing CO2 on the mobile device.
Extracting carbon dioxide (CO2) from ambient air would make it possible to use carbon-based fuels and deal with the associated greenhouse gas emissions after the fact. Since CO2 is neither poisonous nor harmful in parts per million quantities, but creates environmental problems simply by accumulating in the atmosphere, it is possible to remove CO2 from air in order to compensate for equally sized emissions elsewhere and at different times.
Various methods and apparatus have been developed for removing CO2 from air. In one prior art method, air is washed with a sorbent such as an alkaline solution in tanks filled with what are referred to as Raschig rings that maximize the mixing of the gas and liquid. The CO2 reacts with and is captured by the sorbent. For the elimination of small amounts of CO2, gel absorbers also have been used. Although these methods are efficient in removing CO2, they have a serious disadvantage in that for them to efficiently remove carbon dioxide from the air; the air must be driven past the sorbent at fairly high pressures. The most daunting challenge for any technology to scrub significant amounts of low concentration CO2 from the air involves processing vast amounts of air and concentrating the CO2 with an energy consumption less than that that originally generated the CO2. Relatively high pressure losses occur during the washing process resulting in a large expense of energy necessary to compress the air. This additional energy used in compressing the air can have an unfavorable effect with regard to the overall carbon dioxide balance of the process, as the energy required for increasing the air pressure may produce its own CO2 that may exceed the amount captured negating the value of the process.
Such prior art methods result in the inefficient capture of CO2 from air because these processes heat or cool the air, or change the pressure of the air by substantial amounts. As a result, the net loss in CO2 is negligible as the cleaning process may introduce CO2 into the atmosphere as a byproduct of the generation of electricity used to power the process.
The present invention in one aspect provides an improvement over prior art systems for removal of CO2 from air by the utilization of solid phase anion exchange membranes for the direct capture of CO2 and other acid gases such as NOx and SO2 from air. Specifically, this invention provides practical physical configurations of the active element, processes for the manufacture of the active element and configurations options of an air collector device to facilitate the direct capture of CO2 and other acid gases from the air based on solid phase, anion exchange materials.